linux-kernel - Re: [PATCH v2 2/2] sched

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Message-ID: <CAKfTPtDE2rWbRouf8zRyM3UpTfK1k_xrWmvAs-zfoRZqM3zGsw@mail.gmail.com>
Date: Mon, 8 Jul 2024 08:37:06 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Tejun Heo <tj@...nel.org>
Cc: rafael@...nel.org, viresh.kumar@...aro.org, linux-pm@...r.kernel.org, 
	void@...ifault.com, linux-kernel@...r.kernel.org, kernel-team@...a.com, 
	mingo@...hat.com, peterz@...radead.org, David Vernet <dvernet@...a.com>, 
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH v2 2/2] sched_ext: Add cpuperf support

On Sun, 7 Jul 2024 at 03:44, Tejun Heo <tj@...nel.org> wrote:
>
> Hello,
>
> On Sat, Jul 06, 2024 at 11:01:20AM +0200, Vincent Guittot wrote:
> > > There's scx_enabled() and scx_switched_all(). The former is set when some
> > > tasks may be on sched_ext. The latter when all tasks are on sched_ext. When
> > > some tasks may be on sched_ext but other tasks may be on fair, the condition
> > > is scx_enabled() && !scx_switched_all(). So, the above if statement
> > > condition is true for all cases that tasks may be on CFS (sched_ext is
> > > disabled or is enabled in partial mode).
> >
> > My point is that if there is no fair task, cpu_util_cfs_boost() will
> > already return 0 so there is no need to add a sched_ext if statement
> > there
>
> I see, but scx_switched_all() is a static key while cpu_util_cfs_boost()
> isn't necessarily trivial. I can remove the conditional but wouldn't it make
> more sense to keep it?

I prefer to minimize (if not remove) sched_ext related calls in the
fair path so we can easily rework it if needed. And this will also
ensure that all fair task are cleanly removed when they are all
switched to sched_ext

Thanks
Vincent

>
> Thanks.
>
> --
> tejun